Polymeric films are used in a wide variety of packaging applications, including food packaging, pharmaceutical products and non-perishable consumer goods. Films suitable for each of these applications are typically required to exhibit a range of physical properties. Food packaging films in particular may be required to meet numerous demanding performance criteria, depending on the specific application, such as protection from the environment, resistance to physical and environmental abuse during processing, storage and distribution, and an aesthetic and attractive appearance. Optical properties such as high gloss, high clarity, and low haze contribute to the aesthetic consumer appeal of products wrapped in such packaging materials. Good optical properties also permit adequate inspection of the packaged product during the distribution cycle and by the end-user at point of purchase.
In the case of perishable products, such as oxygen sensitive products, oxygen barrier characteristics are required to provide extended shelf life for the packaged product. Limiting the exposure of oxygen-sensitive products to oxygen maintains and enhances the quality and shelf life of many products. For instance, by limiting the oxygen exposure of oxygen-sensitive food products in a packaging system, the quality of the food product can be maintained and spoilage retarded. In addition, such packaging also keeps the product in inventory longer, thereby reducing costs incurred from waste and having to restock.
In the food packaging industry, several techniques for limiting oxygen exposure have been developed. Common techniques include those where oxygen is consumed within the packaging environment by some means other than the packaged article or the packaging material (e.g., through the use of oxygen scavenging sachets), those where reduced oxygen environments are created in the package (e.g., modified atmosphere packaging (MAP) and vacuum packaging), and those where oxygen is prevented from entering the packaging environment (e.g., barrier films).
Sachets containing oxygen scavenging compositions can contain iron compositions, which oxidize to their ferric state, unsaturated fatty acid salts on an absorbent, ascorbic acid and its salts and/or a metal-polyamide complex. The disadvantages of sachets include the need for additional packaging steps (to add the sachet to the package), the potential for contamination of the packaged article should the sachet break, and the danger of ingestion by a consumer.
Oxygen scavenging materials also have been incorporated directly into the packaging structure. This technique (hereinafter referred to as “active oxygen barrier”) can provide a uniform scavenging effect throughout the package and can provide a means of intercepting and scavenging oxygen as it passes through the walls of a package, thereby maintaining the lowest possible oxygen level throughout the package. Active oxygen barriers have been formed by incorporating inorganic powders and/or salts as part of the package. However, incorporation of such powders and/or salts can degrade the transparency and mechanical properties (e.g., tear strength) of the packaging material and can complicate processing, especially where thin films are desired. Also, in some cases these compounds as well as their oxidation products can be absorbed by food in the container, which can result in the food product failing to meet governmental standards for human consumption.
In addition, various films have been developed to help provide oxygen barrier properties to the packaging. For example, ethylene vinyl alcohol copolymer (EVOH) has been known as a good oxygen barrier material, and has been used in the past in conjunction with multilayer packaging films. However, many of these films although providing some level of barrier to oxygen may still permit some oxygen to pass through the film and enter the package. As a result, the film may not provide the desired level of oxygen barrier properties. Accordingly, there still exists a need for films having active oxygen barrier properties.